Lately, it is strongly demanded to reduce a fuel consumption of an automobile in connection with a worldwide effluent control of carbon dioxide associated with a growing interest in environmental problems. In order to cope with such a demand, it is demanded to reduce a rolling resistance as a tire performance. As a means for reducing the rolling resistance of the tire, it is effective to use a rubber composition having a smaller loss tangent (tan δ) and a low heat buildup as a rubber composition applied to a tread portion of the tire.
On the other hand, it is known that a heat buildup of a rubber composition is lowered by substituting the whole or a part of carbon black in the rubber composition using carbon black as a filler with silica, and the rolling resistance of the tire is reduced and the low fuel consumption is improved by using such a silica-containing rubber composition in the tread portion of the tire. Also, it is known that the steering stability on the wet road is simultaneously improved with the improvement of the low fuel consumption when the silica-containing rubber composition is used in the tread portion of the tire. Therefore, it is presumed that the steering stability on the wet road and low fuel consumption of the tire can be highly improved by using in the tread portion of the tire the rubber composition wherein the amount of silica compounded is increased.
However, when the amount of silica compounded is highly increased in the rubber composition, there is a problem that it is difficult to highly disperse the silica into the rubber component and the loss tangent (tan δ) of the rubber composition cannot be sufficiently lowered due to the poor dispersion of silica. Also, since the dispersibility of silica as a filler is bad, there is a problem that the resulting rubber composition is insufficient in the fracture characteristics. Therefore, there is now required a technique capable of sufficiently ensuring the dispersibility of silica into the rubber component even if the amount of silica compounded is large.